Fuel oil gasification burner



March 1966 o. GOLDMANN ETAL 3,238,991

FUEL OIL GASIFIGATION BURNER Filed Nov. 20, 1963 5 Sheets-Sheet l 5 INVENTORS:

G ro MM m IMM March 8, 1966 o. GOLDMANN ETAL 3,238,991

FUEL OIL GASIFICATION BURNER Filed Nov. 20, 1963 3 Sheets-Sheet 2 l I Ill 1 lhl IN V EN TOR I lam am, 118 Hu -Sh t g ev, mm NW March 8, 1966 GOLDMANN ETAL 3,238,991

FUEL OIL GASIFIGATION BURNER Filed Nov. 20, 1965 3 Sheets-Sheet 5 Fig. 6

INVENTORS= ML, WM

BY-. 8 l 1 s M, QJMKMVM United States Patent Office 3,238,991 Patented Mar. 8, 1966 3,238,991 FUEL 01L GASIFICATION BURNER Otto Goldmann, Kiefernweg 26, Wolfenhuttel, Germany;

Otto Himstedt, Heinrich-Heine-Strasse 19, Brannschweig, Germany; and Erhard Schwarze, Pawelstrasse 7, Braunschweig, Germany Filed Nov. 20, 1963, Ser. No. 325,008 Claims priority, application Germany, Nov. 23, 1962, Sch 32,373 20 Claims. (Cl. 158-5) This invention relates to a fuel oil gasification burner. In contrast to conventional fuel oil burners, a fuel oil gasification burner is a burner wherein the oil fog is not burned directly with a luminous flame but wherein a fuel gas mixture comprising oil fog and air is burned with non-luminous blue flame. In such so-called blue burners, it is well-known to inject oil by means of a high pressure nozzle centrally into a Venturi-shaped mixing chamber so as to form a spray cone. Furthermore, it is well known to blow air into the narrowest cross section of the mixing chamber by means of a blower. By appropriate deflectors a rotating movement about the axis of the mixing chamber is imparted to this air. In the prior art oil gasification burners of this type the fine particles of the oil fog are seized by the rotating air stream from the blower, and are flung by centrifugal force against the walls of the mixing chamber, so that a vaporization and gasification of the oil particles can take place. In order to support this process, provision is made in the prior art fuel oil gasification burners of this type, for hot waste gas exhausted from the periphery of the flame to be mixed with the air. In the prior art, this is effected by utilizing the suction effect of the Venturishaped mixing chamber, namely in that suction orifices for hot waste gas are provided in the narrowest cross section thereof.

In all prior art fuel oil gasification burners, the vaporization and gasification process is initiated in that the oil fog produced by spraying, and composed of more or less large oil particles, is flung or sprayed against a hot wall of a mixing chamber or against a hot baffle plate, so that the oil particles vaporize int-o combustible oil vapor or gasified oil.

It has been found, however, that carbonization occurs on the hot wall, surfaces in contact with the oil fog, resulting in deposition of residues which increase during operation. Primarily, this is the result of a decomposition process wherein the fuel is degraded with carbon being extracted and remaining as a residue on the hot wall surfaces.

An object of this invention is, because of this danger of carbonization, to avoid direct contact of the oil fog with hot portions of the Walls and still effect complete vaporization and gasification of the fuel oil particles. The invention is based on the discovery that the smaller the fuel oil particles of the oil fog and consequently the less their. surface area, the more quickly they can be vaporized and at lower temperatures. Consequently the invention seeks to produce a low pressure zone in front of the high pressure nozzle and within a circulating annulus of waste gas-air mixture heated by the waste gas. In this zone, the fuel oil particles of the oil fog emanating from the nozzle can be disintegrated at once, and be converted into fuel oil vapor and gasified oil without contact with the walls.

In accordance with our invention this object is attained in that the hot waste gas is supplied to the intake side of the blower and that the mixing chamber flares with a cone angle larger than the angle of the spray cone of the fuel oil and is so dimensioned that the rotating air shell is guided along the walls of the mixing chamber without changing from laminar to turbulent flow. By feeding the hot waste gas to the blower and notas in the prior artexh-austing it by injector action of the Vent-urishaped mixing chamber, a low pressure zone resulting from the Venturi effect is maintained in front of the nozzle. A further factor producing a low pressure zone in front of the nozzle results from the blower air rotating about the axis of the mixing chamber. Because of the strongly flaring shape of the mixing chamber, this air has the opportunity to form a cyclone-like rotating air shell, which completely surrounds the spray cone of the nozzle and has a core, in which low pressure prevails. In this core of the air shell heated by waste gas, the fuel oil particles are vaporized and gasified very quickly, so that a fuel gas mixture composed of air, waste gas and fuel oil vapor is formed in the mixing chamber.

With normal high pressure nozzles a spray cone of about 30 is produced. In order to attain the effect described, the cone angle of the mixing chamber must be 80, whereas usually a Venturi-tube flares at an angle of 78. It is important, however, that the rotating air shell is guided along the walls of the mixing chambers and does not change from laminar to turbulent flow, as otherwise uncontrollable turbulences occur which prevent the formation of a low pressure core.

To obtain an air shell rotating in the mixing chamber at an angular rate as large as possible, provision can be made for the blower to deliver air into an air guiding channel surrounding the axis of the nozzle in spiral shape and continuously narrowing, from which an air swirl coaxial with the nozzle enters the narrowest portion of the mixing chamber perpendicularly to the plane of the spiral through a narrowing annular passage. Such an arrangement is more effective than the provision of inclined deflectors in the blower air stream.

Advant-ageously the annular passage is formed between the conical wall portion of the mixing chamber upstream from the narrowest portion thereof, and a conical shell surrounding the nozzle. The conical shell about the nozzle can be made axially movable, in order to be able to change the exit cross section and thereby to adjust the air velocity. The conical shell of the nozzle offers still another advantage. A fresh air stream cooling the nozzle can be provided between the nozzle and the shell. The high pressure nozzle is filled with fuel oil also in the times when the burner is out of operation, so that it is advisable to keep the nozzle cooled so that no carbonization of the nozzle can occur. Particular advantages result, if the fuel gas mixture composed of fuel oil vapor, fresh air and waste gas are supplied through a conduit provided outside the mixing chamber to a burner unit mechanically separated from the mixing chamber. Then the heat of the flame is not transferred to the walls of the mixing chamber which, thereof, can remain relatively cool. Advantageously the waste gas percentage is so dimensioned that the fuel gas mixture and also the walls of the mixing chamber are held at a temperature of 200400 C. Provision must, however, be made that the conduit for the fuel gas mixture is also maintained at this temperature, so that the fuel oil vapor does not cool down and condense. Preferably this is achieved by guiding the fuel gas mixture in a conduit along the outer surface of the mixing chamber, which, for example, forms an annular chamber surrounding the walls of the mixing chamber. Furthermore, the waste gas sucked in by the blower from the periphery of the burner unit can be guided along the walls forming said conduit, so that it does its share in keeping the conduit hot.

It is advantageous to enclose the whole burner housing with a heat insulating layer, in order to keep the cooling down during short interruptions of the operation as low as possible.

Preferably the fresh air intake rate of the blower is adjustable. Thereby, the ratio of hot waste gas and fresh air containing oxygen can be changed and adapted to the fuel oil quantity sprayed into it.

As the blower is thermically loaded by the exhausting of hot waste gases, it is advantageous to make provision to avoid a heating of the bearings and of the drive motor.

According to our invention, an electric heating device is provided in the air conduit between blower and mixing chamber, and this heating device is actuated by a thermostat depending on the temperature of the air entering the mixing chamber. Thereby the heating of the air by addition of hot waste gas is replaced during a short warmup period by an electric heating device. With such an electric warm up, a very simple and reliable control of the fuel oil gasification burner is obtained. A solenoid valve governing the oil supply to the high pressure nozzle is controlled from the thermostat, so that fuel oil is supplied to the burner only after the blower air has been heated.

In the following specification, the invention is explained in detail with reference to a preferred embodiment. In the drawings:

FIG. 1 shows a vertical sectional view of a burner,

FIG. 2 shows a sectional view along line II-II of FIG. 1,

FIG. 3 shows a sectional view along line IIIIII of FIG. 2,

FIG. 4 shows a plan view of the burner,

FIG. 5 shows a sectional view along line V-V of FIG. 1,

FIG. 6 shows another embodiment of the blower.

In a burner housing 1 open at the top, at the bottom and on one side and coated on the outside with a heat insulating layer 2, a trough 3 is provided which is affixed to the open side of the burner housing 1 with a flange 3'. At the top, the trough 3 is closed by a screen-like burner insert 4 (as a flame stabilizing grid at the base of a combination zone 42), and is so mounted in the burner housing 1, that waste gas channels 5, 5, 5", are formed between the trough 3 and the burner housing 1. Waste gas channels 5, 5', 5" are open at the top around burner insert 4. In the lower part of the burner housing, the waste gas channels 5, 5, 5" open into an intake opening 6 of a blower 7, which is inserted into the burner housing 1 from below and is aflixed thereto by means of a flange 7'. A fresh air intake pipe 8 opens centrally in the intake opening 6. The intake pipe 8 extends laterally out of the burner housing 1. A butterfly valve 9 adjustable from the outside is provided in the fresh air intake pipe 8.

A mixing chamber body 10 is inserted into the trough 3 from the side. This body has an outlet opening 10 and is affixed to the trough 3. The mixing chamber body 10 defines a mixing or gasification chamber 11 and is provided with a Venturi like structure comprising inner and outer conical, outwardly flaring wall portions 12, 13 respectively on both sides of its narrowest cross section 11' forming a throat. Said flaring wall portions and throat defining an injection opening. The wall portions 12, 13 are in the form of truncated cones connected at their tops, i.e. at the portion thereof defining throat 11. The cone angle A (FIG. 3) formed by the wall portions 12 is about 75. A threaded collar 14 is inserted into the mixing chamber body 10 from the side and is afiixed thereto by means of a flange 14'. A shell body 15 which is conically tapered in its front portion 15' is screwed into the threaded collar 14 from the outside by means of a hollow nut projection 15". The conical shell body 15 together with the conical wall portion 13 of the mixing chamber body form an adjustable annular slot 16 which narrows in the downstream direction. An internallly threaded sleeve 18 is held by spider 17 centrally in the shell body 15. A high pressure nozzle 19 is screwed into said sleeve in such a manner that its opening lies substantially in the narrowest portion 11 of the mixing chamber 11. Between the conical end 15 of shell body 15 and the head of the high pressure nozzle 19, a narrow annular slot 20 is formed. A channel body 22 having its upper end in communication with the mixing chamber body 10 is connected at its lower end to the output socket 7" of the blower 7. In this channel body 22 and in the mixing chamber body 10 a continuously narrowing air supply channel 21 is formed, which inside the mixing chamber body 10 spirals around the shell body 15 (FIG. 5). The air stream delivered by the blower 7 into this air supply channel gets a continuously increasing velocity due to the continuous narrowing of the channel, and, because of the spiral shape, gets a rotating movement about the shell body 15, before it enters the mixing chamber 11 in the narrowest portion thereof through the annular slot 16 as a cyclone-like air swirl.

The blow-er 7 is driven by a motor 23 which is supported on a bridge 24 aifixed to the flange 7'. The drive shaft of the blower 7 is formed as a hollow shaft 25 provided with radial air intake openings 26. A fuel oil pump 27 is connected to the motor 23. The pump 27 is connected to an oil pressure pipe 28 leading to the high pressure nozzle 19. A solenoid valve 28' is arranged in the oil pressure pipe 28. Reference numeral 27' designates the oil intake pipe and numeral 27 designates the return pipe of .the oil pump 27.

An electric heating device 29 (FIG. 5) and a thermostat 30 provided with a switch 30' are mounted in the air supply channel 21 within the channel body 22. The mode of operation of the fuel oil gasification burner described is as follows:

In order to start the cold burner the motor 23 and the heating device 29 are switched on. The solenoid valve 28 remains closed, so that the oil pump delivers oil eX- clusively into the return pipe 27". At first, the blower sucks in only fresh air through the channels 5, 5, 5" and the fresh air intake pipe 8, and discharges this air into the air supply channel 21. In the manner described, this blower air stream enters the mixing chamber 11 through the annular slot 16 as a rotating, cyclone-like air swirl. This air is guided along the conical wall portion 12 of the mixing chamber body 10 and consequently expands centrifugally. Consequently, in the core of this air swirl in front of the nozzle 19, a low pressure zone is produced. This air stream is heated up in the air supply channel 21 by the electric heating device 29, until a temperature of about 250 C. is reached. At this temperature of the air stream the thermostat 30 responds, and the switch 30' thereof actuates a relay (not shown). By this relay, the heating device is switched off, and the solenoid valve 28 is opened. Now oil is sprayed, as indicated at 41, through nozzle 19 at a spray angle B of about 30 into the low pressure core of the air swirl heated up to 250 centigrade. The spray cone of the oil swirl is completely surrounded by the rotating hot air shell so that no oil can reach the walls of the mixing chamber body 10. In the low pressure core of the air swirl, the oil particles are vaporized or gasified quickly and completely, so that a fuel gas mixture composed of oil vapor or gas and air is produced. This mixture enters the trough 3 through opening 10' of the mixing chamber body 10, and is directed by trough 3 about the outside of the mixing chamber body 10 to the burner insert 4. Upon leaving the screen-shaped burner insert 4, the fuel gas mixture is ignited by an electric ignition device 31, and burns in the combustion zone 42 above the screen with blue flame. The discharge velocity of the fuel gas mixture must, of course, be selected with respect to the flame-propagation velocity to prevent flashback of the flame.

Now hot waste gas is sucked in by the blower 7 through waste gas intake channels 5, 5, 5", and gets into the blower 7 through the intake opening 6. In this manner waste gas flowing along the outside of trough 3, keeps the trough hot and the cold fresh air sucked in by the blower 7 through the fresh air intake pipe 8 is heated at least to about 250 centigrade. Thus, the heating device 29 can be kept switched off during the normal operation time of the burner. By sucking in the waste gas in the intake opening 6 an additional injector effect is achieved, whereby a relatively large quantity of fresh air can be sucked in through the relatively narrow fresh air intake pipe 8. By means of the value 9, the fresh air input can be adjusted, and thereby the ratio of waste gas to fresh air can be changed. The velocity of the air swirl blown into the mixing chamber, which velocity depends on the discharge velocity of the fuel gas mixture,

is adjustable by axially shifting the shell body 15, whereby the annular slot 16 is reduced or increased.

Due to the low pressure prevailing in front of the nozzle 19 a small cold fresh air stream is sucked in through the annular slot 20 between the nozzle 19 and the shell body 15. This stream serves to cool the nozzle 19 and to prevent a carbonization at the nozzle 19;.

As the blower 7 is heated by the sucking-in of the hot waste gases, additional cold fresh air is sucked in through the openings 26 and the hollow shaft 25, so that the motor 23 and the bearings of the blower 7 remain cool.

The blower can, as has been shown in FIG. 6, be designed so that a double-faced blower wheel 32 is provided which discharges into a single common outlet 33. On the drive side there is an intake opening 34 for fresh air and on the other side of the blower wheel there is the waste gas intake opening 6. As the drive motor 23 and the drive shaft are positioned completely within the fresh air zone, a cooling air stream through the shaft thereof is then unnecessary. Alternatively, in order to put the fuel oil gasification burner into operation from cold state thereof, the oil fog emanating from the nozzle can be ignited within the mixing chamber during a short heating-up period. As the blower injects only fresh air,

a jet-of-flame-like, soot-free combustion is obtained in.

the mixing chamber because of the high excess of oxygen. After this has happened, the oil supply can be interrupted for a short time, and then the fuel oil can again be injected into the heated mixing chamber without being ignited. Then the resulting fuel gas mixture can be supplied to the burner unit and can be ignited there.

The invention is claimed as follows:

1. In a fuel oil gasification burner, comprising a high pressure nozzle through which oil is injected through a Venturi-shaped intake opening flaring into a mixing and gasifying chamber so as to form a spray cone, and a blower blowing air into the narrowest portion of the chamber, the air making a rotating movement, the oil being vaporized in the chamber to form a combustible mixture with the air which mixture is then conveyed to a combustion zone and burned producing a flame and wherein hot waste gas is exhausted from the periphery of the flame and mixed with said air, the improvement comprising, passageway means to supply the hot waste gas to the intake side of the blower, said mixing chamber flaring with a cone angle larger than the angle of the spray cone of the fuel oil and being so dimensioned and positioned that a shell of rotating air is guided along the walls of the mixing chamber without changing from laminar to turbulent flow.

2. A fuel oil gasification burner according to claim 1, characterized in that the cone angle of the flare of the mixing chamber ranges from 60 to 80.

3. In a fuel oil burner means of the type having a burner body with walls defining a gasification chamber into which the fuel oil is injected from a high pressure nozzle means to be vaporized with the assistance of added heat without combustion in the chamber, with the vapor then being conducted to a separate combustion zone in 6 which it is burned, the improvement comprising: one of said walls defining an injection opening in the shape of a truncated cone defining an axis and a given apex angle and having its circular top at the exterior of the chamber with said one wall flaring outwardly from said cone top in the direction of the opposite wall of the chamber; said nozzle means being smaller in diameter than said circular top, being positioned along said axis with its injection end being about at said top and directed into said chamber, said nozzle means producing a conical shaped spray having an apex angle substantially less than said given apex angle; means, including a blower and an enclosure about said circular top, to inject heated primary air at high velocity into said opening at its top with the air rotating about said axis.

4. In a fuel oil burner as' set forth in claim 3, wherein said blower is spaced from said walls defining said chamber, and said last mentioned means includes an intake opening positioned to receive hot gases of combustion from said zone and a conduit to carry said hot gases along said Walls to the intake of the blower.

5. In a fuel oil burner as set forth in claim 4, wherein said last mentioned means includes a fresh air conduit leading to the intake of the blower and at the blower intake said conduit discharging centrally of the hot gas conduit.

6. In a fuel oil burner as set forth in claim 4, wherein said blower includes a motor, a blower wheel, and a hollow shaft connecting the motor and wheel, said shaft opening into the wheel and having radial air intake openings spaced from the wheel into which cooling air is sucked by'the blower.

7. In a fuel oil burner as set forth in claim 4, wherein said blower includes a double faced blower wheel and casing having two intake openings and one discharge opening, said conduit communicating withone intake opening of the blower, and a fresh air conduit communicating with the other intake opening of the blower.

8. In a fuel oil burner as set forth in claim 3, wherein said last mentioned means includes an electric heating device between the blower and the chamber, and a thermostat positioned to respond to the temperature of the air entering the chamber and connected to the device to control the operation of the same.

9. In a fuel oil burner as set forth in claim 8, including a solenoid valve connected to the nozzle to control the supply of oil thereto, and means connecting said valve to the thermostat to control the operation of the valve in response to the thermostat.

10. In a fuel oil burner means of the type having a burner body with walls defining a gasification chamber into which the fuel oil is injected from a high pressure nozzle to the vaporized with the assistance of added heat without combustion in the chamber, with the vapor then being conducted to a separate combustion zone in which it is burned, the improvement comprising: one of said walls defining a Venturi-shaped injection opening about an axis and having a throat with the walls at each side of said throat being in the shape of truncated cones flaring outward-1y both on the chamber side of the throat and on the opo-psite side of the throat; said nozzle being positi-oned along said axis, spaced from said one wall, and at said opposite side of the throat with the injection end thereof about at said throat and directed into said chamber, said nozzle having means to define a conical shaped spray having an apex substantially less than the apex angle of the truncated cone, defined by said wall on the chamber side of the throat; and means, including a blower, to inject heated primary air into said space between the nozzle and the one wall with the air rotating about said axis.

111. In a fuel oil burner as set forth in claim 10, wherein said last mentioned means includes an intake opening positioned to receive hot gases of combustion from said zone, and fresh air intake openings, with the hot gases and fresh air being mixed to form said heated primary air, and including means to vary the proportion of fresh air to hot gases.

12. In a fuel oil burner as set forth in claim 11, wherein said burner includes a sleeve surrounding the nozzle between the nozzle and inside of said wall at said opposite side, said sleeve having a downstream, with respect to the direction of air flow, end positioned upstream from said throat.

13. In a fuel oil burner as set forth in claim 12, wherein said primary air passes between said sleeve and said wall, and the interior of said sleeve is open to atmosphere at a point spaced from said downstream end for the passage of air thereth-rough.

14. In a fuel oil burner as set forth in claim 12, wherein said burner includes means whereby the sleeve may be moved axially to change the position of said end thereof with respect to the throat.

'15. In a fuel oil burner as set forth in claim 11, wherein said body walls also define a passage from said chamber to said zone and a conduit from said intake opening for hot gases to said blower, at least one wall being common to said conduit and passage whereby said one wall is heated by said hot gases and in turn heats the mixture of primary air and vaporized oil.

16. In a fuel oil burner as set forth in claim 11, Wherein the intake openings are proportioned so that the mixture of heating primary air and hot gases may be varied in temperature from 200 to 400 centigrade.

-17. A fuel oil burner comprising: a generally cylindrical shell about an axis and defining a gasification chamber, said shell having an outlet opening in the bottom thereof adjacent one end, walls at the other end of said shell defining a Venturi-shaped injection opening having a throat normal to said axis with the walls at each side of the throat being in the shape of truncated cones having said axis as the altitude thereof, said throat as the top and the bases spaced from said throat, said truncated cone on the chamber side having a given apex angle; a trough member enclosing said shell except for an open top on the trough member, said shell being spaced from the sides of the shell; a flame stabilizer across the open top of the trough member; a high pressure nozzle means to direct a spray of fuel oil into said chamber and having an injection end positioned Within said Venturi-shaped opening and directed into said chamber coaxial with said axis, said nozzle means having a spray angle substantially less than said apex angle; means to inject heated primary air through said Venturi-shaped opening under pressure and to cause said air to rotate about said axis as it is injected, whereby a combustible mixture of primary air and gasified fuel oil is formed in said chamber, which mixture flows through said outlet opening and out through said flame stabilizer; and means beyond the flame stabilizer, in the direction of such flow, to ignite said combustible mixture.

18. A fuel oil burner comprising: a generally cylindrical shell about an axis and defining a gasification chamber, said shell having an outlet opening in the bottom thereof adjacent one end, walls at the other end of said shell defining a Venturi-shaped injection opening having a throat normal to said axis with the walls at each side of the throat being in the shape of truncated cones having said axis as the altitude thereof, said throat as the top and the bases spaced from said throat; a trough member enclosing said shell except for an open top on the trough member, said trough being spaced from the sides of the shell; a flame stabilizer across the open top of the trough member; a high pressure nozzle means to direct a spray of fuel oil into said chamber and having an injection end positioned within said Venturi-shaped opening and directed into said chamber coaxial with said axis; means to inject heated primary air through said Venturi-shaped opening under pressure and to cause said air to rotate about said axis as it is injected, whereby a combustible mixture of primary air and gasified fuel oil is formed in said chamber, which mixture flows through said outlet opening and out through said flame stabilizer;

and mean-s beyond the flame stabilize-r, in the direction of such flow, to ignite said combustible mixture.

19. In the method of burning fuel oil in a burner of the type wherein the fuel oil is sprayed into a gasification chamber wherein it is vaporized and mixed with primary air to form a combustible mixture with the mixture then being conducted to a combustion zone and burned, the improvement comprising the steps of: heating the primary air to a temperature of between 200 and 400 C.; injecting the heated primary air into the chamber in a vortex of conical configuration with the apex at the side of the chamber and the base at the interior of the chamber; and spraying the oil into the chamber from a point adjacent said apex with the oil being directed generally along the axis of the cone and directed toward the base thereof, said oil being sprayed with a spray angle that is substantially less than the apex angle of the cone.

20. In the method as set forth in claim 19, wherein gases of combustion are withdrawn from the combustion zone and mixed with the primary air in such proportions as to heat the primary air to the specified temperature.

References Cited by the Examiner UNITED STATES PATENTS 653,166 7/1900 Cary 158-5 687,535 11/1901 Machlet 1581 1,101,790 6/1914 Doherty 158-1 1,564,866 12/1925 Leslie 15853 1,592,120 7/ 1926 Meier 15853 1,629,253 5/1927 Breese 1585 1,729,763 10/1929 DeFlorez 158l 2,000,733 5/1935 Avery l58-36 2,110,209 3/1938 Engels 158l FOREIGN PATENTS 690,650 6/1930 France.

JAMES W. WESTHAVER, Primary Examiner. MEYER PERLIN, Examiner.

S. W. MILLARD, Assistant Examiner. 

1. IN A FUEL OIL GASIFICATION BURNER, COMPRISING A HIGH PRESSURE NOZZLE THROUGH WHICH OIL IS INJECTED THROUGH A VENTURI-SHAPED INTAKE OPENING FLARING INTO A MIXING AND GASIFYING CHAMBER SO AS TO FORM A SPRAY CONE, AND A BLOWER BLOWING AIR INTO THE NARROWEST PORTION OF THE CHAMBER, THE AIR MAKIG A ROTATING MOVEMENT, THE OIL BEING VAPORIZED IN THE CHAMBER TO FORM A COMBUSTIBLE MIXTURE WITH THE AIR WHICH MIXTURE IS THEN CONVEYED TO A COMBUSTION ZONE AND BURNED PRODUCING A FLAME AND WHEREIN HOT WASTE GAS IS EXHAUSTED FROM THE PERIPHERY OF THE FLAME AND MIXED WITH SAID AIR, THE IMPROVEMENT COMPRISING, PASSAGEWAY MEANS TO SUPPLY THE HOT WASTE GAS TO THE INTAKE SIDE OF THE BLOWER, SAID MIXING CHAMBER FLARING WITH A CONE ANGLE LARGER THAN THE ANGLE OF THE SPRAY CONE OF THE FUEL OIL AND BEING SO DIMENSIONED AND POSITIONED THAT A SHELL OF ROTATING AIR IS GUIDED ALONG THE WALLS OF THE MIXING CHAMBER WITHOUT CHANGING FROM LAMINAR TO TURBULENT FLOW. 